What do mitochondria do?
Quick answer
Mitochondria are tiny structures inside cells that produce most of a cell’s ATP (adenosine triphosphate), the molecule cells use for energy. They do this through cellular respiration, using oxygen to break down sugars and fats. That’s why they’re nicknamed the “powerhouse of the cell.” Unusually, they carry their own DNA.
How mitochondria make energy
Mitochondria have two membranes. The inner one is folded into ridges called cristae, which give it a huge surface area for energy-making machinery.
| Step | Where | What happens |
|---|---|---|
| Glycolysis | Cell fluid (cytoplasm) | Glucose is split; a little ATP is made |
| Krebs cycle | Inside the mitochondrion | Fuel is broken down further, releasing carbon dioxide |
| Electron transport chain | Inner membrane | Uses oxygen to produce most of the ATP |
Overall, one glucose molecule can yield around 30–32 ATP molecules. That’s why we breathe in oxygen and breathe out carbon dioxide.
How many are there?
It depends on how much energy a cell needs:
| Cell type | Mitochondria |
|---|---|
| Heart muscle | Thousands per cell; they fill about a third of the cell’s volume |
| Liver | Around 1,000–2,000 per cell |
| Mature red blood cells | None |
The heart’s constant work is explained in how many chambers the human heart has.
Once free-living bacteria
Mitochondria have their own circular DNA, and they divide on their own, much like bacteria. Biologist Lynn Margulis championed the endosymbiotic theory in 1967: about 1.5–2 billion years ago, a larger cell swallowed a bacterium that went on living inside it. Over time, they became partners. Plant cells’ chloroplasts likely formed the same way.
Passed down from mothers
You inherit your mitochondria almost entirely from your mother, because the egg contributes them, not the sperm. Scientists use mitochondrial DNA to trace ancestry and human migration.
More than power plants
Mitochondria also help control cell death (apoptosis), store calcium and produce heat. For how cells copy themselves, see why cells divide. For the molecule that carries genes, see what DNA is.
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